A portable version of BL is possible.

I used the EVO 4Gs resolution as example to build an interface prototype. Clicking the "M" activates a drop down menu for your usual options (Save, load, quit, admin, etc). The "B" opens up the brick pallet so you can select different bricks. The items up top are fairly self-explanatory, just click to activate. Clicking the paint palet expands it temporarily so colors are easier to select. The brick menu lets you swipe through to select bricks from your brick selection, clicking picks the brick and activates build placement mode if you aren't in it already. Build-mode (not pictured) positions a transparent brick control set of arrows that let you move bricks horizontally, vertically, and lets you spin them.
The real challenge involved in building a Blockland for a mobile device is the engine. I'm not sure if you can get TGE working on a mobile device. If not, all of the optimizations that make BL possible would have to be remade. Badspot and Kompressor would be remaking the game from scratch in that case. A quick glance at the Torque site shows no signs of this happening soon. They have a version for Apple products though.
A more probably alternative would be to create a side-scrolling type of Blockland. It could be made in one of several engines available for mobile devices (perhaps even browser-based). Dare I say you could have more interactive physics in a 2-D environment?